1. Field of the Invention
The invention relates to the field of telecommunications, and in particular, to call signaling and processing for early media service control.
2. Description of the Prior Art
Telecommunication carriers often times provide early media services to their customers. An early media service is a service that is provided early in the call provisioning process. For example, custom call tones are considered early media. In the case of custom call tones, a calling party dials a called party. Rather than apply a standard call tone to the calling party, such as a ring, a carrier applies a custom call tone, such as a song. The custom call tone is typically selected by the called party as part of a subscription service.
In some early media situations, early media is provided by a third-party provider and a one-way backward call path must be cut through from the third party through the terminating switch to the calling party. In such a case, a calling party goes off-hook and dials the called party. A switch in the originating network generates and transmits an initial address message (IAM) to the terminating network indicating the calling party and the called party. The terminating network recognizes that the call requires early media. Responsively, the terminating network generates and transmits an IAM to a third-party provider. The terminating network simultaneously rings the called party.
Typically, the third-party provider returns an address complete message (ACM) in response to the IAM from the terminating network. The ACM triggers the terminating network to transmit the ACM to the originating network. The ACM causes the one-way backward call path to be cut through from the third-party provider to the calling party. Once the one-way backward call path is open, the third-party provider plays out the early media.
Eventually, the called party answers the call by going off-hook. The off-hook triggers the terminating network to switch connections from the third-party provider to the called party. Additionally, the terminating network signals the originating network to open a two-way bearer path between the calling party and the called party.
Recently, Voice Over Internet Protocol (VOIP) service has increased in popularity. Several signaling protocols, such as the session initiation protocol (SIP) and H.323, are used to support VOIP service. In contrast with circuit-switched networks, most VOIP networks do not apply call tones to calling parties. Rather, call tones are generated and played out locally to the caller by the calling device in response to a signaling message from a central call processing system, such as a soft-switch. In one example, a SIP 180 message triggers a calling device to play-out a ring call tone.
In the prior art, it was recognized that VOIP service must support early media services. In response, the SIP 183 message was designed to trigger a calling device to listen for early media on a port and play-out the early media to the caller.
Often times, VOIP networks interface with circuit-switched networks, such as the public switched telephone network (PSTN). Under such circumstances, interfaces exist to interface between SS7 signaling and VOIP signaling, such as SIP or H.323. Most SS7 signaling messages can be directly interfaced to counter-part SIP messages. For example, a SS7 ACM message is typically mapped to a SIP 180 message. As discussed above, a SIP 180 message triggers the calling device to play-out a locally generated call tone.
More particularly, in order to trigger a SIP 180 message, a SS7 ACM message must be formatted in a manner that maps to the SIP 180 message. For example, a SS7 ACM indicating a Called Party Status of FREE triggers a SIP 180 message.
Likewise, a SS7 ACM message must be formatted in a different manner that maps to a SIP 183 message in order to trigger the generation and transmission of an SIP 183 message to a calling device. For example, a SS7 ACM with the Called Party Status set to NO INDICATION will trigger a SIP 183 message in the VOIP network. This is necessary to provide early media services to VOIP callers that place calls to called parties in SS7 networks.
In an example of successfully provisioning an early media service between a SS7 network and a VOIP network, a VOIP caller sends a SIP INVITE message to a soft-switch. The soft-switch responsively transmits an IAM to a switch in the SS7 network. The switch in the SS7 network responsively forwards the IAM to a third-party early media provider while simultaneously ringing the called party. In response to the IAM, the third-party provider returns an ACM with the Called Party Status set to NO INDICATION. The switch receives and forwards the ACM to the soft-switch, thereby cutting a one-way backward call path to the VOIP network. The soft-switch receives the ACM, responsively maps the ACM to a SIP 183 message, and transmits the SIP 183 message to the calling device. The SIP 183 message instructs the calling device to listen on a specified port for the early media.
Unfortunately, the ACM generated and transmitted by the third-party service provider is not always formatted correctly. For instance, it is a common problem that the third-party service provider formats the ACM with the Called Party Status set to FREE, thereby triggering a SIP 180 message in the VOIP network, rather than a SIP 183 message. Similar problems exist with respect to other third-party services that the signaling generated by the third-party service incorrectly impacts downstream service processes. It is typically too expensive and difficult for a carrier to request third-party service providers to change the signaling that incorrectly impacts downstream service processes.